Controlled synthesis and structure characterization of nanostructured MnWO4

Using Mn to partly substitute the W in W18O49 nanowires, the synthesis of MnWO4 hubnerite nano-cocoons is described in this paper, by using mixed MnCl2 and WCl6 as the precursors and cyclohexanol as the solvent, in a simple solvothermal process. Detailed characterization of the resulting products, using electron microscopy and spectroscopy, has shown that the gradual increase of MnCl2 concentration changes the long W18O49 nanowires to cocoon-like nanomaterials of stable MnWO4 phase. The driving force for such transformations is attributed to the Mn2+ inclusion within the W18O49. At low Mn2+ concentration, internal stresses would be introduced to the W18O49 nanowires; whilst at high Mn2+ concentration close to the stoichiometric composition of MnWO4, the formation of the nano-cocoons is triggered by the intrinsic crystalline feature of the hubnerite. It is believed that a combination of the initial nanowire nucleation and competing growth, and of self-assembly of neighboring parallel nanowires, leads to the final structure.